In general, a fuel cell system is a type of electric power generation system which generates electrical energy through an electrochemical reaction between hydrogen and oxygen (oxygen included in air) by a fuel cell. For example, the fuel cell system may be applied to a fuel cell vehicle and may drive the vehicle by operating an electric motor.
The fuel cell system includes a stack which is an electricity generating assembly configured by unit fuel cells each having an air electrode and a fuel electrode, an air supply device which supplies air to the air electrode of the fuel cell, and a hydrogen supply device which supplies hydrogen to the fuel electrode of the fuel cell.
Meanwhile, in the case of a polymer fuel cell, an appropriate amount of moisture is required to allow an ion exchange membrane of a membrane-electrode assembly (MEA) to smoothly perform functions thereof, and to this end, the air supply device of the fuel cell system includes a humidifier for humidifying air to be supplied to the fuel cell.
The humidifier humidifies dry air, which is supplied by an air compressor of the air supply device, by using moisture in hot and humid air discharged from the air electrode of the fuel cell, and supplies the humidified air to the air electrode of the fuel cell.
As the fuel cell vehicle may have limitations with respect to packaging, a membrane humidification method, which requires a relatively small volume, is applied. The humidifier according to the membrane humidification method has an advantage in that no particular power is required, as well as an advantage in respect to packaging.
The humidifier according to the membrane humidification method performs the membrane humidification through a gas-to-gas moisture exchange method between hot and humid discharge gas discharged from the air electrode of the fuel cell and dry air supplied by the air compressor.
Meanwhile, water produced in the stack clogs a part of, or the entire, air flow path (a stack manifold, an inlet and an outlet of the cell, respective channels in the cell, or the like) of the stack, and thus hinders the supply of the reactant gas, which may cause a deterioration in performance of the stack and a problem with durability of the stack.
Therefore, the humidifier is typically positioned at a lower end of the stack in view of a layout of the fuel cell system. In this case, water condensed in the stack mostly flows by gravity toward the humidifier positioned adjacent to the stack.
In addition, moisture vapor is condensed due to a temperature difference from outside air when the air humidified by the humidifier is supplied to the stack, the condensate water flows by gravity into the humidifier when a flow velocity of the air is low, the moisture vapor is condensed after shutdown, and the condensate water flows into the humidifier from the stack or pipes.
However, because a flow velocity of air to be supplied from the humidifier to the stack is increased when the fuel cell system rapidly outputs power or outputs high power in an idle state of the fuel cell vehicle, the condensate water stagnating in the humidifier flows into the stack and thus closes the flow paths in the stack, which may cause a phenomenon in which the cell is withdrawn from the stack.
The above information disclosed in this Background section is only for enhancement of understanding the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.